Hydraulic motor or pump with constant clamping force between rotor and

Abstract

A hydraulic axial piston motor or pump (8) of the type in which a rotor (10) has an odd-numbered plurality of cylinder ports (30) with which the arcuate ports (40,42) of a port plate (36) successively register. The port plate (36) is provided with fluid exchange ports (44,46) through which cylinders (16) communicate with a hydraulic capacitance system (81,82,84,86,93). The capacitance system (81,82,84,86,93) urges fluid into each cylinder (16) of the rotor (10) through an exchange port (44) after the associated cylinder port (30) has departed from registration with one arcuate port (40) but before the associated piston (14) has reached its bottom-dead-center position (72), and receives fluid from each cylinder through an exchange port (46) after the associated piston has begun its compression stroke but before the cylinder port has begun to register with a second arcuate port (42). Urging fluid into each cylinder eliminates cavitation effects that would otherwise result from having too large a decompression zone (68- 67), while receiving fluid from each cylinder prevents excessive pressurization that would otherwise result from having too large a precompression zone (67). The invention thus enables the use of arcuate ports (40,42) which subtend the more limited angular ranges required to provide a pump or motor that operates with a constant number of high-pressure cylinders and, consequently, with a constant clamping force between the rotor (10) and the port plate (36).